It has long been recognized that it is necessary or desirable to have valves and valving apparatus that result in a good seal when the valve or valving apparatus is in its closed position. This is particularly true when such valves or valving apparatus are desired to be utilized in ultra high vacuum systems. It has also been recognized that the gate valve due to its clear aperture and its short length between flanges is highly desirable for such vacuum applications. It is also desirable to utilize a valve which does not have an elastomeric type seal since such a seal is generally not useful in ultra high vacuum systems due to outgassing and sensitivity to bake-out at higher temperatures used in the process to remove gas and facilitate the reduction of pressure. Consequently, an all metal valve is desired for such ultra high vacuum use.
It is known in the prior art that it is desirable to utilize some type of noble metal coating on appropriate portions of metal valves in order to assist in effecting a good seal when the valve or valving apparatus is in its closed position. For instance, U.S. Pat. No. 1,771,043 discloses a valve with a metal valve closure member that is provided with a seat that is composed of a noble metal. U.S. Pat. No. 4,044,993 discloses a high vacuum gate valve in which the valve closure member is plated with gold plating. This gold plating deforms under force to provide a fluid tight seal when the valve closure member is in the seated position. Unfortunately, with the type of valve apparatus shown in this patent, the gold plating does not remain in its original position on the valve closure member after the valve closure member is subjected to repeated use. Instead, the gold plating tends to flow away from the location on the valve closure member that comes into contact with the valve seat. As a consequence, the valve will begin to leak after it has been subjected to repeated use and such a valve has a very limited life. After such a valve has been subjected to a few hundred cycles, the noble metal coating has been so progressively squeezed out from between the mating surface that it is so thin as to be ineffective to effect a statisfactory seal. At that time such a valve must be replaced or repaired by replating the noble metal onto the appropriate portion of the valve closure member.
The valve and valving apparatus of this invention overcomes the problems associated with such prior art valves that utilize noble metal coatings on sealing surfaces and with the valve and valving apparatus of this invention, it is possible to have a valve that can be subjected to thousands of cycles without any diminished ability to properly provide a seal when the valve or valving apparatus is in its closed position.